Chapter 14 - Energy Generation in Mitochondria and Chloroplasts

Question 1

Which activated carrier contains a high-energy bond whose hydrolysis releases a large amount of free energy?

• ATP
• water
• NADH
• glucose
• high-energy electrons

Answer 1

ATP

(The energy released by the hydrolysis of ATP to ADP can be harnessed to drive many otherwise energetically unfavorable chemical reactions in cells.)

Question 2

Which of these processes require a membrane?

• generation of energy by mitochondria
• generation of ATP by photosynthesis in bacteria
• generation of ATP by photosynthesis in plants
• generation of ATP by oxidative phosphorylation
• generation of ATP by glycolysis

Answer 2

• generation of energy by mitochondria
• generation of ATP by photosynthesis in bacteria
• generation of ATP by photosynthesis in plants
• generation of ATP by oxidative phosphorylation

(The generation of ATP by oxidative phosphorylation differs from the way ATP is produced during glycolysis in that it requires a membrane-bound compartment, such as mitochondria. A related membrane-based process produces ATP during photosynthesis in plants and photosynthetic bacteria.)

Question 3

What is true of the organelles that produce ATP in eukaryotic animal cells?

• They evolved from bacteria engulfed by ancestral cells billions of years ago.
• They harbor eukaryotic-like biosynthetic machinery for making RNA and protein.
• They contain the same genes as the chloroplasts of plant cells.
• They have a separate set of DNA that contains many of the same genes found in the nucleus.
• They reproduce sexually.

Answer 3

They evolved from bacteria engulfed by ancestral cells billions of years ago.

(Mitochondria reproduce in a manner similar to most prokaryotes, harbor bacterial-like biosynthetic machinery for making RNA and proteins, and retain their own genomes. Such facts are considered evidence of their bacterial ancestry.)

Question 4

True or False:

The presence of DNA, as well as bacteria-like machinery for making RNA and proteins, is evidence of the prokaryotic ancestry of these organelles.

Answer 4

True

Question 5

Which part of the mitochondrion contains the proteins that carry out oxidative phosphorylation?

Answer 5

The inner mitochondrial membrane

(The inner mitochondrial membrane, which is folded into cristae, contains the proteins that carry out oxidative phosphorylation, including the electron-transport chain and the ATP synthase that makes ATP.)

Question 6

Which activated carriers are produced by the citric acid cycle?

• NADH
• FADH2
• NADPH
• ATP
• GTP
• CO2

Answer 6

NADH
FADH2
GTP

(NADH and FADH2 donate their high-energy electrons to the electron-transport chain in the inner mitochondrial membrane. The citric acid cycle also produces GTP, an activated nucleoside triphosphate closely related to ATP.)

Question 7

The movement of electrons through the electron-transport chain in mitochondria does which of the following?

• produces oxygen
• produces NADH
• pumps ATP across the inner mitochondrial membrane
• pumps protons out of the mitochondrial matrix
• consumes ATP

Answer 7

pumps protons out of the mitochondrial matrix

(Protons are pumped across the inner mitochondrial membrane and out of the mitochondrial matrix against their electrochemical gradient. This stores energy in an electrochemical gradient that can be used by ATP synthase to power the production of ATP.)

Question 8

When protons move down their electrochemical gradient into the mitochondrial matrix, what do they do?

• produce NAD+
• move electrons through the respiratory chain
• produce NADH
• consume ATP
• produce ATP

Answer 8

Produce ATP

(The passage of protons down their electrochemical gradient through ATP synthase causes the enzyme to produce ATP from ADP and Pi.)

Question 9

Which of the following statements are true of electron transfer in the electron-transport chain?

• NADH has a relatively high electron affinity and initiates the electron-transport process.
• Electrons move toward molecules with a high redox potential.
• NADH is a strong electron donor.
• Each electron transfer is an oxidation–reduction reaction.
• When an electron carrier accepts an electron, it becomes oxidized.

Answer 9

• Electrons move toward molecules with a high redox potential.
• NADH is a strong electron donor.
• Each electron transfer is an oxidation–reduction reaction.

(All electron transfers represent redox reactions. NADH is a strong donor of electrons, and electrons move toward molecules with a high redox potential, which translates into a high affinity for electrons.)

Question 10

During electron transport, which serves as a ready source for protons that can be pumped across the membrane?

• ATP
• glucose
• H2O
• NADH
• O2

Answer 10

H2O

The protons in water are highly mobile, and they are able to move rapidly from one water molecule to another.

Question 11

When the difference in redox potential between two molecules is highly positive, what is true of the transfer of electrons between them?

• It is accompanied by a rise in ΔG.
• It produces ATP.
• It is highly favorable.
• It requires an input of energy.
• It is highly unfavorable.

Answer 11

It is highly favorable.

(A highly positive difference in redox potential translates into a large negative free-energy change (ΔGo) for the transfer of electrons—a reaction that is thus highly favorable.)

Question 12

Most of the energy for the synthesis of ATP comes from which molecule?

• NADH produced by glycolysis
• NADH produced by the citric acid cycle
• FADH2 produced by the citric acid cycle
• NADH produced by the conversion of pyruvate to acetyl CoA
• GTP produced by the citric acid cycle

Answer 12

NADH produced by the citric acid cycle

(One turn of the citric acid cycle produces three molecules of NADH. Because glycolysis produces two molecules of pyruvate, six NADHs will be produced per molecule of glucose oxidized.)

Question 13

Stage 1 of photosynthesis is, in large part, equivalent to what process?

• glycolysis
• the production of acetyl CoA by the pyruvate dehydrogenase complex
• oxidative phosphorylation
• the citric acid cycle
• the carbon-fixation cycle

Answer 13

Oxidative phosphorylation

(In this stage of photosynthesis, the movement of electrons along an electron-transport chain is used to generate a proton gradient that can be used by ATP synthase to produce ATP. The same mechanism occurs during oxidative phosphorylation.)

Question 14

When an electron is removed from the reaction center of photosystem II, the missing electron is replaced by an electron from which of the following?

• H2O
• H+
• photosystem I
• sunlight
• manganese

Answer 14

H2O

Photosystem II includes a water-splitting enzyme that extracts electrons from water, producing O2 as a by-product.

Question 15

In this simplified diagram of the reactions of the carbon-fixation cycle, which step is catalyzed by the enzyme Rubisco?

• A
• B
• C
• D
• E

Answer 15

E

(In the first reaction of the carbon-fixation cycle, here labeled step E, Rubisco catalyzes the addition of CO2 to a five-carbon molecule of ribulose 1,5-bisphosphate to produce two three-carbon molecules.)

Question 16

What is true of stage 2 of photosynthesis?

• It takes place in the chloroplast grana.
• It generates a proton gradient across the thylakoid membrane.
• It produces all of the O2 we breathe.
• It begins with the production of ATP and NADPH and ends with their consumption.
• It produces glyceraldehyde 3-phosphate in the stroma.

Answer 16

It produces glyceraldehyde 3-phosphate in the stroma.

(In stage 2 of photosynthesis, which begins in the stroma, the ATP and the NADPH produced in stage 1 are used to drive the manufacture of glyceraldehyde 3-phosphate from CO2.)

Question 17

What is one reason that plants do not generally produce sugars after dark?

• O2 is unavailable after dark.
• The enzymes involved in stage 2 of photosynthesis are inactivated in the dark.
• The enzymes involved in stage 1 of photosynthesis are inactivated in the dark.
• CO2 is unavailable after dark.
• The enzymes involved in stage 2 of photosynthesis are inactivated in the light.

Answer 17

The enzymes involved in stage 2 of photosynthesis are inactivated in the dark.

(In addition to requiring the ATP and NADPH produced by the light-dependent reactions in stage 1 of photosynthesis, several of the enzymes required for carbon fixation are inactivated in the dark and reactivated by light-stimulated electron transport.)

Question 18

The first living cells on Earth—whether prokaryotes or primitive eukaryotes—most likely generated ATP by what process?

• aerobic cell respiration
• fermentation
• oxidative phosphorylation
• photosynthesis
• nitrogen fixation

Answer 18

Fermentation

(In fermentation, organic molecules are broken down to generate energy without the involvement of oxygen. Such processes likely provided energy for the earliest cells on the planet.)

Question 19

During Earth’s history, with the rise of cyanobacteria, what molecule began accumulating in the atmosphere for the first time?

• CO2
• H2O
• O2
• N2

Answer 19

O2

(The availability of O2 made possible the evolution of nonphotosynthetic organisms that used aerobic metabolism to make their ATP.)

Question 20

What is true of the evolution of electron transport systems?

• They are a relatively recent evolutionary innovation.
• They are evolutionarily ancient and likely provided energy for the earliest cells on Earth.
• In ancient prokaryotes, they did not require the use of a membrane.
• Their requirement for oxygen as an electron acceptor means they evolved first in photosynthetic prokaryotes.
• The earliest ones involved using H2O as an electron donor.

Answer 20

They are evolutionarily ancient and likely provided energy for the earliest cells on Earth.

(Membrane-based mechanisms for the generation of energy appeared very early in the history of life, more than 3 billion years ago.)

Question 21

Antibiotics should inhibit bacterial cell growth without generating side effects in the human patient, but that is not always the case. Some antibiotics that inhibit bacterial protein synthesis by binding to bacterial ribosomes induce negative side effects in patients. What is the most likely cause of these side effects?

• The antibiotics interfere with chloroplast ribosomes.
• The antibiotics interfere with cytoplasmic ribosomes.
• The antibiotics interfere with ribosomes attached to the ER, impairing RER function.
• The antibiotics interfere with mitochondrial ribosomes.

Answer 21

The antibiotics interfere with mitochondrial ribosomes.

(Mitochondria are of bacterial origin and contain ribosomes more similar to bacterial ribosomes than the ribosomes found in the eukaryotic cell cytoplasm. Antibiotics that target bacterial cell wall synthesis do not induce mitochondrial side effects.)

Question 22

To explore how yeast cells metabolize glucose, investigators use a DNA microarray to examine the effect the sugar has on the expression of a variety of genes. Cultured yeast cells are supplemented with high concentrations of glucose. mRNAs are extracted from the cells, converted into cDNAs, and labeled with a fluorescent marker. The samples are then hybridized to a DNA microarray that includes probes representing yeast genes.

Shown here is a data set representing genes involved in ribosome biogenesis and electron transport. Red indicates that supplementing the growth medium with glucose has increased the expression of the genes, whereas green indicates that the added glucose has decreased gene expression.

Based on this data, what can be concluded about how yeast cells behave when grown in the presence of high concentrations of glucose?

• Yeast cells shut down protein synthesis when grown in the presence of high concentrations of glucose.
• Yeast cells exposed to high concentrations of glucose grow by fermentation.
• Yeast cells grow poorly in high concentrations of glucose.
• Yeast cells consume large amount of oxygen as they break down glucose.
• Yeast cells are able to extract the maximum amount of energy from glucose via oxidative phosphorylation.

Answer 22

Yeast cells exposed to high concentrations of glucose grow by fermentation.

(Yeast cells grown in the presence of high glucose concentrations decrease the expression of genes that encode components of the electron-transport chain. This suggests that, under these conditions, the cells are not relying heavily on oxidative phosphorylation to break down glucose and generate ATP.)

Question 23

Protons are pumped across the mitochondrial inner membrane as electrons are transferred through the mitochondrial electron transport chain. Which of the following statements about proton pumping are correct?
Choose one or more:

• The NADH dehydrogenase, cytochrome b-c1, and cytochrome oxidase complexes all pump protons across the membrane.
• The mitochondria use the proton gradient to synthesize ATP.
• Protons are pumped into the matrix of the mitochondria.
• The pH inside the mitochondrial matrix is higher than in the intermembrane space.

Answer 23

• The NADH dehydrogenase, cytochrome b-c1, and cytochrome oxidase complexes all pump protons across the membrane.
• The mitochondria use the proton gradient to synthesize ATP.
• The pH inside the mitochondrial matrix is higher than in the intermembrane space.

(The NADH dehydrogenase, cytochrome b-c1, and cytochrome oxidase complexes all pump protons from the matrix to the intermembrane space, which results in a higher pH inside the matrix. The mitochondria then use the energy of the proton gradient to synthesize ATP.)

Question 24

Antimycin A is a piscicide (fish poison) used to manage fisheries and kill invasive species. Antimycin A blocks the transfer of electrons through the cytochrome b-c1 complex. What components of the electron transport chain are bound to high-energy electrons after treating a mitochondrion with antimycin A?

• All three complexes and NADH are bound to high-energy electrons.
• None of the complexes are bound to high-energy electrons.
• O2 and the cytochrome c oxidase complex are bound to high-energy electrons while NADH and the NADH dehydrogenase complex are not.
• NADH and the NADH dehydrogenase complex are bound to high-energy electrons while O2 and the cytochrome c oxidase complex are not.

Answer 24

NADH and the NADH dehydrogenase complex are bound to high-energy electrons while O2 and the cytochrome c oxidase complex are not.

(The molecules before the blockage will still bind high-energy electrons after electron transfer. No transfer of high-energy electrons will occur to molecules that come after the blockage and these molecules will not be bound to high-energy electrons.)

Question 25

True or False:

The passage of protons through the H+ carrier causes the carrier and the central stalk to spin rapidly.

Answer 25

True

Question 26

The drug 2,4-dinitrophenol (DNP) makes the mitochondrial inner membrane permeable to H+. The resulting disruption of the proton gradient inhibits the mitochondrial production of ATP.

What additional effect would DNP have on the transport of ATP out of the mitochondrial matrix?

• ATP transport will decrease because less ATP will be available to diffuse across the inner membrane.
• ATP export will decrease because its carrier exploits the difference in voltage across the inner membrane.
• ATP transport will increase because ATP synthase will be forced to operate in the “reverse” direction.
• None, because the inner membrane is permeable to ATP.
• None, because ATP export is not coupled to the movement of protons across the inner membrane.

Answer 26

ATP export will decrease because its carrier exploits the difference in voltage across the inner membrane.

(Under normal conditions, the mitochondrial matrix is slightly more negatively charged than the intermembrane space; an antiport carrier exploits this voltage gradient to import ADP and export ATP, which is more negatively charged than ADP.)

Question 27

Investigators introduce two proteins into the membrane of artificial lipid vesicles: (1) an ATP synthase isolated from the mitochondria of cow heart muscle, and (2) a light-activated proton pump purified from the prokaryote Halobacterium halobium. The proteins are oriented as shown in the diagram. When ADP and Pi are added to the external medium and the vesicle is exposed to light, would this system produce ATP?

• Yes, because the proton pump will generate a proton gradient that ATP synthase can use to synthesize ATP.
• No, because ATP synthase is not oriented correctly.
• No, because protons are small enough to pass freely in and out of an artificial lipid vesicle.
• No, because no electron-transport chain is present.
• No, because cows and prokaryotes are so distantly related that their proteins cannot be expected to work together.

Answer 27

No, because ATP synthase is not oriented correctly.

(If the ATP synthase were oriented in the opposite direction, it could take advantage of the proton gradient produced by the pump to generate ATP outside the vesicle. These experiments, performed in the 1970s, demonstrated definitively that a proton gradient could drive the production of ATP.)

Question 28

True or False:

Carriers #1 and #2 are actually part of cytochrome c reductase, carrier #3 is cytochrome c, and carrier #4 is part of the cytochrome c oxidase complex.

Answer 28

True

Question 29

In the mitochondrial matrix, the enzyme _________ can extract electrons from succinate and transfer them to the mobile electron carrier ubiquinone. Ubiquinone then passes them to cytochrome c reductase.

Answer 29

succinate dehydrogenase

Question 30

Order the components involved in electron transport from those with the lowest redox potential to the highest.

Answer 30

Lowest Redox Potential
1. NADH/NAD+
2. NADH dehydrogenase complex
3. cytochrome c reductase
4. cytochrome c oxidase
5. H2O / O2
Highest Redox Potential

(Electrons move from molecules with the lowest redox potential—or lowest electron affinity—to those with the highest redox potential.

Not included in this list are the mobile electron carriers ubiquinone, which has a redox potential between that of NADH dehydrogenase complex and cytochrome c reductase, and cytochrome c, which shuttles electrons between cytochrome c reductase and cytochrome c oxidase.)

Question 31

Not all fat cells are equivalent. Humans and other animals contain both white fat cells and brown fat cells, named after their color. Because increases in brown fat cells may aid weight loss, researchers are interested in factors that control the ratio of white fat cells and brown fat cells, as detailed in a 2017 article in Obesity Reviews. What is the mechanism for how brown fat cells aid weight loss?

• Brown fat cells contain fewer mitochondria than white fat cells.
• Brown fat cells produce a lot of ATP.
• Brown fat cell mitochondria contain an uncoupling protein.
• Brown fat cells express bacteriorhodopsin.

Answer 31

Brown fat cell mitochondria contain an uncoupling protein.

(This uncoupling protein moves protons down their electrochemical gradient, bypassing ATP synthase. Since ATP production is limited, cells continue to burn fat to try to produce ATP.)

Question 32

The proton gradient that drives ATP synthesis during photosynthesis is generated by which of the following?

• an electron carrier that receives electrons from photosystem I
• an electron carrier that removes electrons from water
• an electron carrier that pumps protons out of the thylakoid space into the stroma
• the operation of two photosystems that work in series
• an electron carrier that pumps protons out of the stroma into the thylakoid space

Answer 32

An electron carrier that pumps protons out of the stroma into the thylakoid space

(Cytochrome b6-f complex is the sole proton pump in the photosynthetic electron-transport chain; it uses energy from the transfer of electrons released by photosystem II to pump H+ into the thylakoid space.)

Question 33

Which of the following statements correctly describe an aspect of converting light to chemical energy in chloroplasts?

• The energy in excited electrons is used to pump protons across the thylakoid membrane from the stroma to the thylakoid space.
• Excited electrons are passed through an electron transport chain.
• Photosystem II is used to produce NADPH directly from NADP+ and two electrons.
• Light excites electrons in photosystem II only.

Answer 33

• The energy in excited electrons is used to pump protons across the thylakoid membrane from the stroma to the thylakoid space.
• Excited electrons are passed through an electron transport chain.

(As excited electrons pass through the electron transport chain, the energy of the electrons is used to pump protons across the thylakoid membrane.)

Question 34

What would be the consequences to NADPH production if the redox potential of pC (plastocyanin) were altered to be more negative than the redox potential of cytochrome b6-f?

• NADPH would be broken down since the electron transport chain would work backward.
• NADPH production would halt since pC would no longer accept electrons from the cytochrome b6-f complex, blocking the electron transport chain.
• NADPH production would not be altered since NADPH is produced from photosystem I.
• NADPH production would be higher since pC would be a better electron donor.

Answer 34

NADPH production would halt since pC would no longer accept electrons from the cytochrome b6-f complex, blocking the electron transport chain.

(Making the redox potential of pC more negative would block the ability of pC to accept electrons from cytochrome b6-f. If pC cannot accept electrons, the electron transport chain would halt and NADPH production would be blocked.)

Question 35

Carbon fixation occurs in the second stage of photosynthesis, during the light-independent reactions of the Calvin cycle. In the first step of this cycle, the enzyme Rubisco adds CO2 to the energy-rich compound ribulose 1,5-bisphosphate, ultimately producing two molecules of 3-phosphoglycerate.

In a culture of green alga that is carrying out photosynthesis in the presence of CO2 in the laboratory, what would happen to the levels of ribulose 1,5-bisphosphate and 3-phosphoglycerate in the minutes after the lights were turned off and the cultures were plunged into darkness?

• Ribulose 1,5-bisphosphate would be depleted, but 3-phosphoglycerate would accumulate.
• Ribulose 1,5-bisphosphate would accumulate, but 3-phosphoglycerate would be depleted.
• Nothing would happen because the Calvin cycle is not light-dependent.
• Both would accumulate.
• Both would be depleted.

Answer 35

Ribulose 1,5-bisphosphate would be depleted, but 3-phosphoglycerate would accumulate.

(Rubisco would continue to consume ribulose 1,5-bisphosphate and produce 3-phosphoglycerate. Subsequent reactions in the cycle require ATP and NADPH—both products of the light reactions.)

Question 36

What happens to the ATP produced during stage 1 of photosynthesis?

• It is consumed within the chloroplast to produce glyceraldehyde 3-phosphate.
• It is consumed within the chloroplast to fuel electron transport.
• It is consumed within the chloroplast to produce NADPH.
• It is exported from the chloroplast and used to produce sucrose.
• It is exported from the chloroplast to fuel the plant’s metabolic needs.

Answer 36

It is consumed within the chloroplast to produce glyceraldehyde 3-phosphate.

(The chloroplast membrane is impermeable to ATP; the ATP generated during stage 1 of photosynthesis is thus used to produce sugars during stage 2.)

Question 37

What is true of nitrogen fixation?

• It requires a small energy input and is thus energetically favorable.
• It promoted the evolution of ancient cells by allowing them to convert N2 to NO2 near thermal vents.
• It can be used to generate an H+ gradient.
• It converts CO2 and H2O into sugars.
• It reduces N2 to ammonia (NH3).

Answer 37

It reduces N2 to ammonia (NH3).

The resulting NH3 is then used to build amino acids, nucleotides, and other nitrogen-containing organic molecules.

Question 38

The buildup of lactic and formic acids generated by anaerobic fermentation likely favored the evolution of which of the following?

• hydrothermal vents
• eukaryotic cells
• cells that could use the energy of sunlight to produce NADPH
• cells that could pump protons
• multicellular life

Answer 38

Cells that could pump protons

(A buildup of such acids would have lowered the pH of the environment, favoring the survival of cells that could pump H+ out of the cytosol, preventing their interiors from becoming
too acidic.)